Which of the following reactions is used to prepare Haloarenes?

The correct answer is Option (4) → Sandmeyer reaction

• Sandmeyer reaction is used to prepare haloarenes from arenediazonium salts:

$ArN_2^+Cl^- + CuX \rightarrow ArX + N_2 \quad (X = Cl, Br, CN)$

• Stephen reaction → converts nitriles to aldehydes.
• Gattermann-Koch reaction → formylation of aromatic rings (produces aromatic aldehydes).
• Cannizzaro reaction → disproportionation of non-enolizable aldehydes to alcohols and acids.

Hence, the correct answer is Sandmeyer reaction.